Zircon Hf signatures from granitic orthogneisses of the Spanish Central System: Significance and sources of the Cambro-Ordovician magmatism in the Iberian Variscan Belt |
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| Institution: | 1. Departamento de Petrología y Geoquímica, Facultad de Geología, Universidad Complutense de Madrid, c/ José Antonio Novais, 2., 28040 Madrid, Spain;2. Instituto de Geociencias (UCM, CSIC), 28040 Madrid, Spain;3. Department of Geosciences, University of Oslo, 1047 Blindern, N-0316 Oslo, Norway;4. ARC Centre of Excellence for Core to Crust Fluid System/GEMOC, Macquarie University, New South Wales 2109, Australia;1. Department of Geo-Sciences, School of Mining and Metallurgical Engineering, National Technical University of Athens, 9 Heroon Politechniou St, GR-15773, Zografou (Athens), Greece;2. Institute of Petrology and Structural Geology, Charles University, Prague, Albertov 6, 12843 Prague 2, Czech Republic;1. Centre d''Estudis de la Neu i de la Muntanya d''Andorra, Institut d''Estudis Andorrans, Andorra;2. Departamento de Petrología y Geoquímica, Universidad Complutense de Madrid, 28040 Madrid, Spain;3. Departament de Geodinàmica i Geofísica-Institut de Recerca GEOMODELS, Universitat de Barcelona (UB), Martí i Franquès s/n, Barcelona 08028, Spain;4. Departament de Geoquímica, Petrologia i Prospecció Geològica, Universitat de Barcelona (UB), Martí i Franquès s/n, Barcelona 08028, Spain;5. Senckenberg Naturhistorische Sammlungen Dresden, Museum für Mineralogie und Geologie, Sektion Geochronologie, Königsbrücker Landstraße 159, D-01109 Dresden, Germany;1. Shandong Provincial Key Laboratory of Depositional Mineralization & Sedimentary Minerals, Shandong University of Science and Technology, Qingdao 266590, China;2. School of Earth Sciences and Resources, China University of Geosciences Beijing, 29 Xueyuan Road, Beijing 100083, China;3. Department of Earth Sciences, University of Adelaide, Adelaide, SA 5005, Australia;1. Departamento de Mineralogía y Petrología e Instituto de Geociencias (UCM, CSIC), Facultad de Ciencias Geológicas, Universidad Complutense, 28040 Madrid, Spain;2. Dpto. de Geodinámica, Estratigrafía y Paleontología, Facultad de Ciencias Geológicas, Universidad Complutense, 28040 Madrid, Spain;3. Department of Geosciences, Goethe University, 60438 Frankfurt am Main, Germany;1. Instituto Geológico y Minero de España, Ríos Rosas 23, 28003 Madrid, Spain;2. Departamento de Petrología y Geoquímica e Instituto de Geociencias (UCM, CSIC), Universidad Complutense de Madrid, 28040 Madrid, Spain;3. Geology and Geography Department, Tomsk State University, Lenin Street 36, Tomsk 634050, Russian Federation;1. Ecole et Observatoire des Sciences de la Terre, Université de Strasbourg, UMR 7516 of CNRS, 1 rue Blessig, 67084 Strasbourg Cedex, France;2. Center for Lithospheric Research, Czech Geological Survey, Klárov 3, 118 21, Prague 1, Czech Republic;3. Université de Lorraine – Ecole Nationale Supérieure de Géologie, UMR 7359-GéoRessources, 2 rue du Doyen Marcel Roubault, 54518 Vandeuvre-les-Nancy Cedex, France |
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| Abstract: | Metagranitic orthogneisses are abundant in the Central Iberian Zone (CIZ). This felsic magmatism has a highly peraluminous composition (A/CNK = 1.07–1.62) defining a typical S-type granite character, common in crustal thickening environments. The studied Spanish Central System (SCS) orthogneisses yield Late Cambrian to Early Ordovician U–Pb zircon ages (496 to 481 Ma), overlapping with the available literature data (mostly from 477 to 500 Ma). These orthogneisses are intrusive into metasedimentary sequences from the northern CIZ that have been recently dated at about 536 Ma. Late Ediacaran inherited zircons are common in the SCS orthogneisses (10% to 75% of the total zircon population). Most inheritance ranges from Neoproterozoic to Late Mesoproterozoic in age (0.52 to 1.25 Ga) and shows marked positive ?Hft values (>+5). This long period of Proterozoic juvenile input is only recognized in the metasedimentary rocks of the Schist–Greywacke Complex, outcropping in the southern CIZ. The proposed linkage between the southern CIZ metasediments (as sources) and the studied orthogneisses is reinforced by their similar Nd isotopic signatures (from ? 2.81 to ? 4.95) and the highly peraluminous character of the orthogneisses. The intrusion of this felsic magmatism within the northern CIZ, having been generated by melting of the more distal southern CIZ metasediments, together with their recycled crustal origin, suggests crustal thickening of the northern Gondwana margin during a period of flat subduction. The orthogneisses define a large linear S-type magmatic belt cropping out for over 650 km from central Spain to Galicia. The ~ 35 Ma delay between sedimentation and granite intrusion is a typical time interval for crustal thickening models. This thickening stage evolved toward a passive margin setting, allowing the deposition of the siliciclastic Ordovician series which covered the previous terranes. Minor Floian-aged tholeiitic magmatism, giving rise to scarce metabasite outcrops in the SCS, probably postdates thickening and marks this tectonic change in central Iberia. |
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